July 10, 2009

Figure 1. Velocity (km s−1) for the principal component of the Brγ line in each NIFS spaxel derived
from the data with a Gaussian fit to the line profile. The mean Brγ velocity (VLSR = −62.5 km s−1) of
the principal component has been removed from the map. The bipolar structure does not line up with
any known point source, and the axis does not align with the direction of the large scale ionized
flow detected at radio wavelengths. The peak relative velocities are −24 km s−1 and +31 km s−1, but
the color map is “stretched” slightly to show smaller velocities.

Using the Altair adaptive optics system with the Gemini Near-Infrared Spectrograph (NIFS) on Gemini
North, a US/Australian team have obtained unprecedented high-spatial resolution integral field
spectra of the Ultra-Compact H II Region K3-50A. The study reveals never-before-seen morphology and
kinematics within this complex region of star formation (see Figure 1).

The team of Robert Blum (NOAO, Gemini Science Center) and Peter McGregor (Australian National
University) observed the 3 arcsecond NIFS field at the core of the region, (covering 0.1 parsec at
the object’s estimated distance of 7 kiloparsecs). They found sharp density variations that are
thought to result from the action of the high mass central source radiation field and stellar wind on
its birth cocoon and immediate surroundings. The observations were made at the Fredrick C. Gillett,
Gemini North telescope on Mauna Kea, Hawai‘i in July of 2006.

The high angular resolution of the data (~0.2 arcsecond), moderate spectral resolution
(approximately R = 5200), and detection of multiple spectral lines (Brγ, He
I, [Fe III], [Kr III], [Se IV] and H2) allowed a detailed analysis of K3-50A (see Figure 2),
including resolving ionization structure in the HII region as a function of position. Among the
findings of this analysis is a bipolar kinematic feature that is not symmetric about any detected
point source or ionized outflow seen in earlier radio continuum and recombination line studies.
Several possibilities exist to explain the feature. It may be that a lower mass protostar is
associated with the central star of K3-50A and its protostellar outflow is being ionized by the hot
central source. Alternately, the bipolar flow may be the origin of a large-scale outflow seen in the
radio which is re-directed by the material surrounding the compact central source.

K3-50A has a long history of observations that have spanned the spectrum from optical to radio
(though the central source itself is highly obscured at optical wavelengths). The Gemini
observations consist of near-infrared K-band spectra over NIFS’s ~3x3 arcsecond field which is
sliced into 29x69 rectangular spatial pixels (spaxels) for a datacube of 2,001 elements. While this
data cube has provided a detailed look at the nebular structure on a fine spatial scale, the central
source itself remains a mystery. The putative massive young star is still veiled by the intense
nebular continuum arising in its circumstellar environment: even with adaptive optics, no
photospheric features of the star were detected.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Maunakea, Hawai'i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in five partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, the Brazilian Ministério da Ciência, Tecnologia e Inovação and the Chilean Comisión Nacional de Investigación Científica y Tecnológica (CONICYT). The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.